The overall objective of the proposal is to elucidate the role of catechol estrogens in the mammalian reproduction. From the quantitative point of view, catechol estrogens are significant metabolites of estrogens in humans and animals. The investigation will include the content of female sex steroid hormones including catechol estrogens in the pituitary, hypothalamus and reproductive tracts during early development, puberty, reproductive cycle and pregnancy and their relationships with the plasma concentrations of gonadotropins and steroid hormones. The study will also include the effects on the implantation in rabbits following intra-luminal administration of catechol estrogens by means of silastic implants.